general-relativity

How torsion balances, the Apollo 15 feather drop, and the MICROSCOPE satellite tested whether all matter falls alike, now to a few parts per quadrillion.

Mercury has an oversized iron core, ice at its poles, and a day longer than its year. What MESSENGER found and what BepiColombo is due to do in November 2026.

LIGO's first gravitational-wave detection confirmed a century-old prediction of general relativity and opened a new way to observe the universe.

Time moves slower near gravity because mass curves spacetime, and general relativity says clocks deeper in that curvature tick at a measurably slower rate.

When physicists say a singularity exists at the center of a black hole, they do not mean a point of infinite density crammed into zero volume. They mean that the equations of general relativity stop making predictions, and that something beyond those equations is needed. The distinction matters enormously for what singularities are and whether they are real.

On May 29, 1919, two expeditions photographed a solar eclipse to test Einstein's general relativity. The results made Einstein a global celebrity — and sparked a controversy that took 90 years to resolve.

In October 1971, physicists flew atomic clocks around the world and proved time dilation is real — clocks gained and lost nanoseconds exactly as Einstein predicted.

On September 14, 2015, LIGO detected a ripple in spacetime from two merging black holes a billion light-years away. Here is how the instrument works and what it measured.

Wormholes: theoretical tunnels through spacetime. Einstein-Rosen bridges, exotic matter, traversability, ER=EPR, and time travel paradoxes explained.

Two perspectives, one terrifying destination. From spaghettification to the firewall paradox — the real physics of falling into a black hole.